Users of certain types of electronic test equipment, such as oscilloscopes and logic analyzers are frequently faced with a dilemma. The connection to the DUT (Device Under Test) or SUT (System Under Test) must be made through a probe of some sort, but there is almost no room to allow it. For example, while one might connect the 50Ω front panel input of a high bandwidth oscilloscope to the 50Ω front panel output of some microwave signal generator using a length of suitable 50Ω transmission line, to get at some signal location on a densely populated PCB (printed circuit board) it is far more likely that a handheld active probe will be needed. These are expensive and delicate assemblies that generally have a ‘probe pod’ that connects to the front panel of the 'scope, while a cable carries power and a transmission line for the signal from the probe pod to a small handheld probe housing that encloses an amplifier that can drive the transmission line. Generally the amplifier is a differential one with + and − inputs. Sometimes fixed or moveable rigid pins are present for genuine moveable handheld probing at this location and the next. Other times there is no such luxury, as perhaps the PCB cannot be operated on a board extender, and when installed where it belongs there is another board (or a chassis wall) on either side (all on ½ inch centers!). In these cases the user of the 'scope resigns herself to removing the PCB, attaching short ‘flying leads’ to the probe's tip and then soldering the free ends of those leads to the locations to be ‘probed,’ and then carefully re-installing the PCB. This works, but gets to be a major aggravation mighty fast if there are many different locations to be observed during the analysis of some complicated situation.
It was in pursuit of a solution to this aggravation that the subject matter of the incorporated SIGNAL PROBE AND PROBE ASSEMBLY was developed. What is disclosed therein is a two part connector assembly, one part of which is coupled to the probe's input, and the other part to the location to be probed. The part that attaches to the probe input has what is known as a ZIF (Zero Insertion Force) connector. A ZIF connector is a (generally female) connector that includes a manually operated release mechanism for expanding the electrical contact elements of individual sockets or electrical receptacles so that they accept corresponding male pins or lands without noticeable (or at least appreciable) force. Once the male portions are fully inserted the action of the release mechanism is reversed (a lever is moved, a tab is slid, or a button released), and the force needed to bring the male and female contacts into good electro-mechanical contact is then re-applied within the female ZIF connector.
ZIF connectors are commonly used in situations where there are many pins (e.g., a large microprocessor that is to be replaceable in the field) and the cost and likelihood of damage using a standard connector is a prohibitive risk. It is not difficult to appreciate this when contemplating a microprocessor or other large IC (Integrated Circuit) that is two or three inches on a side with perhaps four hundred or more pins. The insertion force for any pin/socket with decent wiping action/gripping force means that, for such a large number of pins, a rather robust force would be needed to install the part. When done manually, the slightest mis-alignment will remain undetected until some pins are bent. Even with good alignment there is still the issue of damage to the PCB or cracking the substrate of the part. Then there is the issue of how to get the old part out. Should it pried out with a screwdriver at one end? Will that crack the socket? Obviating these concerns is what the notion of a ZIF connector is all about.
In the case of SIGNAL PROBE AND PROBE ASSEMBLY the issue is not so much the number of pins, but the mechanical delicateness of the probe tip and the lack of strength in the solder joints used to affix the flying leads to the PCB. (The trace widths on a PCB are often 0.050″ or less—not much to solder to.) The idea is to allow a user to attach as many inexpensive male ‘connection accessories’ with flexible flying leads as needed at any one time to different locations of the PCB. A (female) ZIF connector is hooked up to the probe tip with short flexible extended transmission lines supplied for the purpose. Then the ZIF connector is mated with the appropriate (if more than one) connection accessory and the measurement activity begun. To move the 'scope (or other type of test equipment in use) nothing needs to be unsoldered until all measurement activity is known with confidence to have been concluded.
That is, to perform measurements at other locations the ZIF connector is simply disconnected from one connection accessory and then connected to another. The flexibility of the extended transmission lines and of the flying leads acts as ‘mechanical decoupling’ between the tethering solder joints and the bulky parts of the active probe (cable from the probe pod and the housing for the amplifier), so that accidental movement of those bulky items will be less likely to break a solder joint between a flying lead and the PCB. A ZIF connector is preferred for this service to, well, ‘gorilla-proof’ the operation of disconnecting the probe from one connection accessory and then connecting it to another. Because of the high frequency nature of the signals and the apparatus needed to measure them, certain physical dimensions of things allowed to experience the signals are small, perhaps even tiny. (Some oscilloscope browsers will break under just a few ounces of applied pressure!) Bending over in bad light, hands extended beyond the focus of your glasses, off balance and standing on one foot, it is all too easy to accidently apply too much force to a regular connector and break something. So it is ZIF to the rescue, as it were.
As handy as the apparatus of SIGNAL PROBE AND PROBE ASSEMBLY is, we have found room for an improvement. The style of ZIF connector used in SIGNAL PROBE AND PROBE ASSEMBLY is rated for about twenty uses. After that, its ability to form a reliable connection is degraded. Twenty uses is, in many episodes of troubleshooting or analysis, not very many. Particularly so for something apt to be construed as attached “for the duration” to the business end of an expensive active probe for a wide band digital oscilloscope. Furthermore, attaching and detaching things to that probe is not a nonchalant operation with no risk; done carelessly (or if a gorilla is on the loose) it can damage the probe. We need to look at this problem through the other end of the telescope, as it were, and see what might be done.